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By next summer, Metrorail may need a broader palette of colors. Transit authority staffers have long discussed a proposal to divert some Blue Line trains across the Yellow Line bridge and send them along the Green Line route to Greenbelt. At the same time, they would add trains between West Falls Church and Largo Town Center, a route that includes stations now served exclusively by Orange or Blue line trains. Besides disrupting the color scheme, what would this rerouting accomplish?

Ridership in central Washington is growing fastest on the eastern side, the area served by stations including Navy Yard, Federal Center SW, Gallery Place, Judiciary Square and Union Station. That's where we've seen the construction cranes this past decade, said Jim Hughes, Metro's deputy general manager for operations and strategic planning.

Meanwhile, Metro is cramming all the rush-hour trains it can through the Rosslyn tunnel under the Potomac River. "We are scheduling as many trains as we can through there," Hughes told a Metro board committee this month. "All those trains are packed, and every time there is an incident, a delay of any time, it's taking us forever to recover."

Creating new routes

Metro is proposing to have more trains go where the riders are going. The plan would divert three currently operating Blue Line trains per peak hour from the Rosslyn tunnel by sending them across the other Potomac crossing, the Yellow Line bridge, which has excess capacity. These trains would operate between Franconia-Springfield and Greenbelt.

Because the diversion would clear some extra room at the Rosslyn tunnel, the transit authority would add three trains per peak hour between West Falls Church and Largo, via the tunnel. That should ease some of the crowding on the western end of the Orange Line while compensating for the reduction in Blue Line service between L'Enfant Plaza and Largo.

When the first phase of the Dulles Metrorail extension opens, possibly in 2013, those three trains could start their runs at the new Wiehle Avenue Station. Meanwhile, Hughes said, Metro stands to gain some service reliability by reducing the need to use the Blue/Orange line switch at Rosslyn.

Impact on riders

This highly unusual change in routing would affect riders on every line but the Red Line.

By Metro's estimate, 14,800 riders would see a service improvement. For some, including riders heading toward Greenbelt, Fort Totten or Franconia-Springfield, the benefit would be more frequent and more direct service to the eastern side of downtown. Even a rider who now takes the Blue Line from Franconia-Springfield to Metro Center or Farragut West might have an easier time taking this new service to L'Enfant Plaza and then transferring to the Blue or Orange lines.

Not everyone wins. Blue Line service to Rosslyn would be reduced from 10 to seven trips per peak hour. Metro figures that about 1,100 riders who use the Blue Line from the southern stations to Rosslyn and the western area of downtown would wind up with a longer trip, since there would be three fewer trains per hour for them and gaps between trains of up to 12 minutes.

What's next

Metro's first challenge will be explaining this change to Blue, Orange, Yellow and Green line riders so they don't wind up in the wrong place or miss their connections.

Should the two new services get new colors? Or would it be simpler to keep the current colors and change the destination signs? How should the Metrorail maps be revised to reflect the new route?